How to dwfine a vector function depend on time with userexpression

General
1

I want to define a vector function depend on time wih userexpression. This function will appear in the right hand.And i need to update this function with time step.
code:
class Coeff(UserExpression):
def init(self, t, **kwargs):
super().init(kwargs)
self.t = t

def eval_cell(self, t, value, ufl_cell):
    if self.t <= 2.0:
        value[0] = 2.0
        value[1] = 0.0

    else:
        value[0] = 0.0
        value[1] = 0.0

def value_shape(self):
    return (2,)

errors: UFLException: UFL conditions cannot be evaluated as bool in a Python context.

2

You need to provide a minimal reproducible example, ie an code that anyone can run and reproduce the same error message.